Device for controlling rotational speed of internal combustion engine

ABSTRACT

An engine speed control unit of an internal combustion engine for controlling an engine speed so that it can reach a target value, changes the engine speed so that it can reach a target value in a period of time from the completion of the initial combustion of the engine starting to the idling steady state. The after-start engine speed peak actual value “gnepk”, which is an engine speed in the idling state in a predetermined period of time from the start of the engine, is calculated, and the after-start engine speed peak target value “tnepk” is read in from the map, and the ratio “rnepk” is found. When the ratio “rnepk” is out of the target range, it can be considered that the burning state is bad.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an engine speed control unit forcontrolling the engine speed of an internal combustion engine so that itcan reach a target value.

2. Background Art

It is important to control the engine speed of an internal combustionengine so that it can reach a target value.

For example, in the case of an automobile, in order to purify exhaustgas to be cleaner or in order to improve drivability, it is necessary tocontrol the engine speed of an internal combustion engine so that it canreach the target value in various conditions.

For example, as the engine speed of an internal combustion engine afterthe engine has started greatly affects the exhaust gas, that is, as theengine speed of an internal combustion engine in the period from thecompletion of the initial combustion at starting to the steady state ofidling of the engine greatly affects the exhaust gas, it is necessary tocontrol the engine speed after the start of the engine so that theengine speed can reach the target value.

In this connection, one of the reasons why the engine speed fluctuatesafter the start of an engine is that a failure in burning occurs in acylinder. Accordingly, in order to prevent the engine speed fromfluctuating after the start of an engine, it is necessary to detect theburning state in a cylinder after the engine has started and control theengine speed so that burning can be conducted properly. In order tocontrol the engine speed of an internal combustion engine so thatburning can be conducted properly, Japanese Unexamined PatentPublication No. 62-3139 discloses a device by which the degree ofthrottle opening is controlled to a target value corresponding to thetemperature of an internal combustion engine at the start.

However, when a quantity of suction air is changed in the case of afailure in burning, the burning state is further deteriorated. Thereason is described as follows. The failure in burning at the start ofan engine is caused by a lean air/fuel ratio because fuel is notsufficiently atomized at the start of an engine but adheres onto a wallface of a suction port so that a sufficient quantity of fuel can not beintroduced into a combustion chamber. When the degree of throttleopening is controlled so that it can be increased, negative pressure ina suction tube is reduced, and fuel atomization is further deterioratedand the air/fuel ratio becomes much leaner.

The engine speed of an internal combustion engine in the idling steadystate greatly affects the exhaust gas. Therefore, it is also necessaryto control the engine speed in the idling steady state so that it canreach the target value. In order to accomplish the above object,Japanese Unexamined Patent Publication No. 5-222997 discloses a suitabledevice. In this device, in the case of a failure of the suction airfeedback control system, it is changed over to the ignition timingfeedback control system, and when the engine temperature is low,ignition timing feedback control is subjected to restriction.

In the device disclosed in the above unexamined patent publication, inthe case of a failure of the suction air feedback control system, it ischanged over to the ignition timing feedback control system, however,even if a failure in burning is caused by feedback control conducted bythe suction air feedback control system, it is impossible to detect thefailure in burning.

Even if a load given to the engine is changed, it is necessary to keepthe engine speed at the target value. In order to accomplish the object,Japanese Unexamined Patent Publication No. 59-3135 discloses a device bywhich feedback control is conducted so that the idling engine speed canbe the target value by increasing the rate of control. However,according to the device of the above unexamined patent publication, itis disclosed that the rate of control is increased with respect to thefluctuation of a load given to the engine, however, the device isprovided with only a feedback control means conducted by a quantity ofsuction air. Therefore, it is impossible to conduct feedback controlwith a parameter other than the quantity of suction air.

Japanese Unexamined Patent Publication No. 62-210240 discloses a device.In this device, in the case where the temperature of engine coolant islow, suction air feedback control is stopped and open control isconducted while the suction air is fixed at a value corresponding to thetemperature of engine coolant. This device is characterized in thatlearning is conducted in the case of obtaining a value corresponding tothe temperature of engine coolant. According to the device of the aboveunexamined patent publication, a quantity of suction air in the casewhere suction air feedback control is stopped and open control isconducted can be found by learning, and this open control can complywith a change with time or a difference between each products.

However, even in the process of suction air feedback control, of course,control is affected by the change with time or the difference betweeneach products. Therefore, for example, in the case where the enginespeed is subjected to feedback control by adding a correction value to areference value of suction air quantity, a difference between therequired value and the reference value is increased by the change withtime or the difference between individual bodies. Accordingly, thecorrection value is increased. As a result, it takes a long period oftime for the engine speed to reach the target value.

However, it is impossible for the device of the above unexamined patentpublication to solve the above problems although learning is conductedby the device.

In view of the above problems, it is an object of the present inventionto provide an engine speed control unit capable of controlling theengine speed so that it can reach the target value.

It is another object of the present invention to provide an engine speedcontrol unit capable of controlling the engine speed at the start of theengine so that it can reach the target value. It is still another objectof the present invention to provide an engine speed control unit capableof controlling the engine speed in the idling steady state so that itcan reach the target value. It is still another object of the presentinvention to provide an engine speed control unit capable of controllingthe engine speed so that it can reach the target value even if a loadgive to the engine fluctuates. It is still another object of the presentinvention to provide an engine speed control unit capable of controllingthe engine speed in the idling steady state so that it can reach thetarget value. It is still another object of the present invention toprovide an engine speed control unit capable of removing influences of achange with time and a difference in individual bodies upon feedbackcontrol of the engine speed.

SUMMARY OF THE INVENTION

The present invention provides an engine speed control unit of aninternal combustion engine for controlling an engine speed so that itcan reach a target, comprising: a first engine speed control means forcontrolling the engine speed by changing a quantity of suction air; asecond engine speed control means for controlling the engine speed bychanging a control value of a control parameter except for the quantityof suction air; and a burning state judgment means (also referred to asa means for judging a burning state), wherein the engine speed iscontrolled by the first engine speed control means in the case of a goodburning state, and control by the first engine speed control means isstopped and the engine speed is controlled by the second engine speedcontrol means in the case of a bad burning state.

In the engine speed control unit composed as described above, in thecase of a good burning state, a quantity of suction air is changed bythe first engine speed control means so as to control the engine speed.In the case of a bad burning state, the first engine speed control meansstops controlling, and another control parameter, other than thequantity of suction air, is changed by the second engine speed controlmeans without changing the quantity of suction air, so that the enginespeed can be controlled. Therefore, the quantity of suction air is notchanged and the burning state is not further deteriorated.

According to one aspect of the present invention, after the engine hasbeen set in motion, that is, in a period from the completion of initialcombustion at starting to an idling steady state, the engine speed iscontrolled so that it can reach a target value. Therefore, the firstengine speed control means is made to be a first after-start enginespeed control means for controlling the after-start engine speed, whichis an engine speed from the completion of initial combustion at Startingto the idling steady state, so that the after-start engine speed canshow a target change characteristic in the case where the burning stateis judged to be good, the second engine speed control means is made tobe a second after-start engine speed control means for controlling theafter-start engine speed, which is an engine speed from the completionof explosion at the engine start to the idling steady state, so that theafter-start engine speed can show a target change characteristic in thecase where the burning state is judged to be bad, and the after-startengine speed from the completion of explosion at the engine start to theidling steady state is controlled.

In this case, for example, the second after-start engine speed controlmeans changes at least one of the control values of ignition timing,quantity of fuel injection and fuel injection timing.

Further, an engine speed control unit of an internal combustion enginecomprises a bad burning cylinder judgment means for judging a badburning cylinder, wherein, when it is judged to be a bad burning state,the bad burning cylinder is distinguished from other cylinders andcontrolled by the second after-start engine speed control means so thatthe engine speed can show a target change characteristic.

According to another aspect of the present invention, after the enginehas been set in motion, that is, in a period from the completion ofexplosion to an idling steady state, the engine speed is controlled sothat it can reach a target value. Therefore, the first engine speedcontrol means is made to be a first idling engine speed control meansfor controlling the engine speed in the idling steady state so that itcan reach the target value by feedback control in the case where theburning state is judged to be good, the second engine speed controlmeans is made to be a second idling engine speed control means forcontrolling the engine speed in the idling steady state so that it canreach the target value in the case where the burning state is judged tobe bad, and the engine speed in the idling steady state is controlled sothat it can reach the target value.

In this case, for example, when it is judged to be a bad burning stateand the idling engine speed control by the first idling engine speedcontrol means is stopped and the idling engine speed control by thesecond idling engine speed control means is executed, the feedbackcontrol by the first idling engine speed control means is executed againafter that, the burning state is rejudged by the burning state judgmentmeans in this state and, when it is again judged to be a bad burningstate in the rejudgment of the burning state, the idling engine speedcontrol is executed by the second engine speed control means.

The idling engine speed control executed by the second engine speedcontrol means after the rejudgment of the burning state is conducted bythe same parameter as that of the idling engine speed control executedby the second engine speed control means before the rejudgment of theburning state while the control value is being changed.

The idling engine speed control executed by the second engine speedcontrol means after the rejudgment of the burning state is conducted bya different parameter from that of the idling engine speed controlexecuted by the second engine speed control means before the rejudgmentof the burning state.

The idling engine speed control conducted by the second engine speedcontrol means before the rejudgment of the burning state and the idlingengine speed control conducted by the second engine speed control meansafter the rejudgment of the burning state are executed being selected sothat the idling engine speed control, the influence given to exhaust gasemission of which is smaller, is executed first.

Further, the engine speed control unit of an internal combustion enginecomprises a bad burning cylinder discrimination means for discriminatinga cylinder in a bad burning state, wherein when it is judged to be a badburning state, the bad burning cylinder is discriminated from othercylinders and controlled by the second engine speed control means.

The idling engine speed control conducted by the second engine speedcontrol means is also feedback control.

The idling engine speed control conducted by the second engine speedcontrol means is a quantitative change control by which the controlparameter is changed by a predetermined value so that the controlparameter cannot exceed a guard value.

The internal combustion engine is provided with an air/fuel ratiofeedback control means for controlling an air/fuel ratio by feedbackcontrol, and the idling engine speed is controlled by the first idlingengine speed control means when the air/fuel ratio feedback controlmeans is operated.

The idling engine speed is controlled by the first idling engine speedcontrol means when the engine temperature is higher than a predeterminedvalue.

The idling engine speed is controlled by the first idling engine speedcontrol means when the lapse of time after the start of the engine ismore than a predetermined value.

The burning state judgment means judges a burning state from a change inthe engine speed with respect to a change in the quantity of suction airof feedback control conducted by the first engine speed control means.

According to another aspect of the present invention, in order tocontrol the engine speed so that it can reach the target even when aload given to the engine is fluctuating, the first engine speed controlmeans conducts feedback-control so that the engine speed in the idlingsteady state can be a target value when it is judged to be a goodburning state, and the second engine speed control means continuesfeedback-control so that the engine speed can be an after-load-changeengine speed target value, which has been previously set, when a load ischanged in the process of executing engine speed control by the secondengine speed control means.

In this case, for example, the after-load-change engine speed targetvalue is the same as the before-load-change engine speed target value.

Alternatively, the after-load-change engine speed target value isdifferent from the before-load-change engine speed target value.

Alternatively, an engine speed control unit of an internal combustionengine further comprises a load change detection means, wherein theafter-load-change engine speed target value is determined by a change inthe load.

Alternatively, the after-load-change control reference valuecorresponding to the after-load change engine speed target value is set,and the second engine speed control means conducts feedback control onthe basis of the after-load-change control reference value.

Alternatively, an engine speed control unit of an internal combustionengine further comprises a load change detection means, wherein theafter-load-change control reference value is determined by a change inthe load.

Alternatively, the second engine speed control means conducts feedbackcontrol on the idling engine speed by one of the control parameters ofthe ignition timing and the quantity of fuel injection before a changein the load, and the second engine speed control means conducts feedbackcontrol on the engine speed by the same control parameter as that ofbefore a change in the load even after a change in the load.

According to another aspect of the present invention, in order to removethe influence of a change with time and a difference in individualproducts on the feedback control of the engine speed, an engine speedcontrol unit of an internal combustion engine according to claim 1,further comprises: a parameter reference value learning means forrenewing and storing a parameter reference value according to a state ofoperation; a parameter correction value calculating means forcalculating a parameter correction value necessary for making the enginespeed close to a target value; and a parameter control means forcontrolling a parameter so as to provide a parameter execution value inwhich the parameter correction value is added to the parameter referencevalue, wherein the parameter reference value learning means renews aparameter reference value so that the parameter correction value can bereduced in the case where the parameter correction value exceeds apredetermined range, and the engine speed of the internal combustionengine is controlled so that it can reach a target value by feedbackcontrol of the control parameter selected according to the state ofburning.

In this case, for example, the parameter reference value learning meansstores a parameter reference value according to at least one of theengine temperature, the shift position of a transmission connected withthe engine and the state of operation of the accessories.

Alternatively, a quantity of suction air is selected as a controlparameter in the case of a good burning state.

Alternatively, ignition timing or a quantity of fuel injection isselected as a control parameter in the case of a bad burning state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of control conducted in the first embodiment.

FIG. 2(A) is a view for explaining a burning state judgment in the caseof a bad burning state in control conducted in the first embodiment.

FIG. 2(B) is a view for explaining a burning state judgment in the caseof a good burning state in control conducted in the first embodiment.

FIG. 3 is a flow chart of control conducted in the first variation ofthe first embodiment.

FIG. 4(A) is a view for explaining a burning state judgment in the caseof a bad burning state in control conducted in the first variation ofthe first embodiment.

FIG. 4(B) is a view for explaining a burning state judgment in the caseof a good burning state in control conducted in the first variation ofthe first embodiment.

FIG. 5 is a flow chart of control conducted in the second variation ofthe first embodiment.

FIG. 6(A) is a view for explaining a burning state judgment in the caseof a bad burning state in control conducted in the second variation ofthe first embodiment.

FIG. 6(B) is a view for explaining a burning state judgment in the caseof a good burning state in control conducted in the second variation ofthe first embodiment.

FIG. 7 is a flow chart of control conducted in the second embodiment.

FIG. 8 is a flowchart of control conducted in the third embodiment.

FIG. 9 is a view for explaining a change in injection timing in controlof the third embodiment.

FIG. 10 is a flow chart of control conducted in the fourth embodiment.

FIG. 11 is a flow chart of control conducted in the fifth embodiment.

FIG. 12 is a flow chart of control conducted in the first variation ofthe fifth embodiment.

FIG. 13 is a flow chart of control conducted in the second variation ofthe fifth embodiment.

FIG. 14 is a flow chart of control conducted in the sixth embodiment.

FIG. 15 is a flow chart of control conducted in the variation of thesixth embodiment.

FIG. 16 is a flow chart of control conducted in the seventh embodiment.

FIG. 17 is a flow chart of control conducted in the seventh embodiment.

FIG. 18 is a flow chart of control conducted in the variation of theseventh embodiment.

FIG. 19 is a flow chart of control conducted in the variation of theseventh embodiment.

FIG. 20 is a flow chart of control conducted in the eighth embodiment.

FIG. 21 is a map used for the ignition timing feedback control in thefifth embodiment.

FIG. 22 is a map used for the fuel injection quantity feedback controlin the first variation of the fifth embodiment.

FIG. 23 is a map used for the fuel injection timing control in thesecond variation of the fifth embodiment.

FIG. 24 is a view for explaining a burning state judgment in the suctionair quantity feedback control of each embodiment.

FIG. 25 is a flow chart of control conducted in the ninth embodiment.

FIG. 26 is a flow chart of control conducted in the variation of theninth embodiment.

FIG. 27 is a flow chart of control conducted in the tenth embodiment.

FIG. 28 is a flow chart of control conducted in the eleventh embodiment.

FIG. 29 is a flow chart of control conducted in the twelfth embodiment.

FIG. 30 is a flow chart of control conducted in the variation of thethirteenth embodiment.

FIG. 31 is a flow chart of control conducted in the variation of thefourteenth embodiment.

FIG. 32 is a flow chart of control conducted in the fifteenthembodiment.

FIG. 33 is a flow chart of control conducted in the sixteenthembodiment.

FIG. 34 is a flow chart of control conducted in the seventeenthembodiment.

FIG. 35 is a flow chart of control conducted in the eighteenthembodiment.

FIG. 36 is a view for explaining control conducted in the fifteenthembodiment.

FIG. 37 is a map of dTHA in control conducted in the fifteenthembodiment.

FIG. 38 is a map of dIA in control conducted in the sixteenthembodiment.

FIG. 39 is a map of dTAU in control conducted in the seventeenthembodiment.

FIG. 40 is a map of initial values of GTHA in control conducted in thefifteenth embodiment.

FIG. 41 is a map of initial values of GIA in control conducted in thesixteenth embodiment.

FIG. 42 is a map of initial values of GTAU in control conducted in theseventeenth embodiment.

FIG. 43 is a view showing the structure of hardware common among theembodiments of the present invention.

THE MOST PREFERRED EMBODIMENT

Referring to the accompanying drawings, embodiments of the presentinvention will be explained below.

FIG. 43 is a schematic illustration showing the structure of hardwarethat is common among the embodiments described later. As shown in FIG.43, there is provided an electronic control throttle 3, which is locatedon the downstream side of an air cleaner not shown in the drawing, inthe suction passage 2 of the internal combustion engine 1. In thiselectronic control throttle 3, the throttle valve 3 a is opened andclosed by the throttle motor 3 b. When a command of the degree ofopening is inputted from ECU (engine control unit) 10 into theelectronic control throttle 3, the throttle motor 3 b responds to thiscommand and makes the throttle valve 3 a follow the degree of opening ofthe command.

The throttle valve 3 a is controlled from the fully closed state, whichis shown by a solid line, to the fully opened state which is shown by abroken line. The degree of opening is detected by the throttle openingdegree sensor 4. This degree of opening directed by the command isdetermined by an operating signal of the accelerator pedal (acceleratorpedal opening degree signal) which is sent from the accelerator openingdegree sensor 15, which is attached to the accelerator pedal 14, fordetecting a quantity of operation of the accelerator pedal.

In this connection, it is thoroughly possible to control a quantity ofsuction air by this electronic throttle valve 3 in the process ofidling. However, it is also possible to control a quantity of suctionair by the idling speed control valve (ISCV) 5 which is arrangedbypassing the throttle valve 3 a as shown in the drawing.

On the upstream side of the throttle valve 3 in the suction air passage2, there is provided an atmospheric pressure sensor 18. On thedownstream side of the throttle valve 3 in the suction air passage 2,there is provided a surge tank 6. In this surge tank 6, there isprovided a pressure sensor 7 for detecting pressure of suction air. Onthe downstream side of surge tank 6, there is provided a fuel injectionvalve 8 for supplying pressured fuel from the fuel supply system to thesuction air port of each cylinder. Ignition is conducted at the ignitionplug 29 by the ignition coil 28 according to a signal sent from ECU 10to the igniter 27.

In the coolant passage 9 in the cylinder block of the internalcombustion engine 1, there is provided a coolant temperature sensor 11for detecting the coolant temperature. The coolant temperature sensor 11generates an electric signal, as an analog voltage, corresponding to thecoolant temperature. In the exhaust gas passage 12, there is provided athree way catalytic converter (not shown) which simultaneously purifiesthe three harmful components, HC, CO and NOx, contained in an exhaustgas. In the exhaust gas passage 12 on the upstream side of thiscatalytic converter, there is provided an O₂ sensor 13 which is one ofthe air/fuel ratio sensors. This O₂ sensor 13 generates an electricsignal corresponding to the concentration of the oxygen componentcontained in exhaust gas. The signal generated by each sensor isinputted into ECU 10.

Further, the following signals are inputted into this ECU 10. They are:a key position signal (accessory position, ON-position and starterposition) sent from the ignition switch 17 connected with the battery16; a top dead centre signal TDC sent from the crank position sensor 21arranged close to the timing rotor 24 which is integrated with the crankshaft timing pulley attached to one end of the crank shaft; a crankangle signal CA sent from the crank position sensor 21 at eachpredetermined angle; a reference position signal sent from the camposition sensor 30; and a lubricant temperature sent from the lubricanttemperature sensor 22. The ring gear 23 attached to the other end of thecrank shaft is rotated by the starter 19 when the internal combustionengine 1 is set into motion.

When the internal combustion engine 1 starts operating, ECU 10 ispowered and the program is started, and an output signal sent from eachsensor is accepted by ECU 10. Therefore, ECU 10 controls the throttlemotor 3 b for opening and closing the throttle valve 3 a, and also ECU10 controls the ISCV 5, fuel injection valve 8, igniter 27 and otheractuators. Therefore, ECU 10 includes: an A/D converter for convertingan analog signal, which is sent from each sensor, into a digital signal;an input and output interface 101 into which an input signal is inputtedfrom each sensor and from which an output signal for driving eachactuator is, outputted; CPU 102 for conducting calculation; memoriessuch as ROM 103 and RAM 104; and a clock 105. They are connected witheach other by the bus 106.

In this case, explanations will be made into detection of the enginespeed ne and discrimination of cylinders.

In the timing rotor 24, there are provided signal teeth 25 at each 10°CA. In order to detect the top dead centre, there is provided a no-toothportion 26 in which two teeth are not arranged. Therefore, the number ofthe signal teeth is 34 in the signal teeth 25. The crank position sensor21 is composed of an electromagnetic pickup and outputs a crank rotationsignal at each rotation angle 10°. The engine speed Ne can be obtainedby measuring an interval (time) of these crank angle signals.

On the other hand, the cam position sensor 30 is attached to the camshaft which is rotated by one revolution for two revolutions of thecrank shaft 2. For example, a reference signal is generated by the camposition sensor 30 at the top dead centre of compression of the firstcylinder. In the first embodiment described later, a cylinder in a badburning state is discriminated by measuring the lapse time which haslapsed from the reference signal sent from the cam position sensor 30.

Control of each embodiment of the present invention, the structure ofhardware of which is composed as described above, will be explainedbelow.

In this case, the first to the fourth embodiments will be explained asthe first group.

The fifth to the eighth embodiments will be explained as the secondgroup.

The ninth to the fourteenth embodiments will be explained as the thirdgroup.

The fifteenth to the eighteenth embodiments will be explained as thefourth group.

Embodiments in the First Group

First, embodiments in the first group will be explained below. In eachembodiment in the first group, there is provided an engine speed controlunit for controlling the engine speed so that it can reach the targetvalue without further deteriorating a bad burning state after theinternal combustion engine has been set into motion in a period of timefrom the completion of explosion to the idling steady state.

In each embodiment in the first group, the burning state is judged bywhether or not the engine speed is changing according to the target. Inthe case where the engine speed is not changing according to the target,it is judged that the burning state is bad. Therefore, control exceptfor control of a quantity of suction air is conducted so that the enginespeed can be changed according to the target.

First, as an index to be controlled as a target index, consideration isgiven to the following three indexes to be controlled.

(1) Peak engine speed after the start of the engine

(2) Rate, of change in the engine speed after the start of the engine

(3) Average of the rate of increase in the engine speed after the startof the engine

First, as a control parameter for controlling the index to be controlledso that it can reach the target in the case of a bad burning state,consideration is given to the following three indexes.

(a) Ignition timing

(b) Quantity of fuel injection

(c) Fuel injection timing

The following are successively explained.

First Embodiment:

Index to be controlled (1)+Control parameter (a)

Its First Variation:

Index to be controlled (2)+Control parameter (a)

Its Second Variation:

Index to be controlled (3)+Control parameter (a)

Second Embodiment:

Index to be controlled (1)+Control parameter (b)

Third Embodiment:

Index to be controlled (1)+Control parameter (c)

Fourth Embodiment

Index to be controlled (2)+Control parameter (a)+Cylinder discrimination

The above embodiments are successively explained below.

First Embodiment

In the first embodiment, the operation is conducted as follows. The peakengine speed in a predetermined period after the start of the engine islearned (stored or renewed). When a ratio of this learning value to thetarget value, which is previously determined according to the enginetemperature and stored in ECU 10, is out of the range of the target, itis judged that a bad burning state has occurred. The value of ignitiontiming (command value) of the present time is corrected so that thisratio can be in the range of the target after the next start of theengine, and thus a corrected value is used as the value of the nexttime. Concerning the quantity of suction air (command value), the valueof the present time is also used as the value of the next time, as itis.

In this case, the value of the ignition timing of the next time is foundin such a manner that the ignition timing of the present time ismultiplied by the ratio of the learning value of the peak engine speedto the target value.

FIG. 1 is a flow chart of control conducted in the first embodiment. Instep 1001, it is judged whether or not it is in an idling state. Thisjudgment is conducted by a signal sent from the throttle opening degreesensor 4 or the accelerator opening degree sensor 15. In step 1002, itis judged whether or not it is in a predetermined period of time fromthe start of the engine. This judgment is conducted by a timer which isstarted simultaneously with the start of the engine when it is not truein steps 1001 and 1002, the program proceeds to step 1010 and returns.When it is true in both steps 1001 and 1002, the program proceeds tostep 1003, and the after-start peak engine speed actual value “gnepk” ofthe present time is calculated. In step 1004, the after-start peakengine speed target “tnepk”, which has been set according to the enginetemperature, is read in from the map. In step 1005, the ratio“rnepk”=“tnepk/gnepk” of the after-start peak engine speed actual value“gnepk” found in step 1003 to the after-start peak engine speed targetvalue “tnepk” found in step 1004 is found.

Further in step 1006, it is judged whether or not the ratio“rnepk”=“tnepk”/“gnepk” of the after-start peak engine speed actualvalue “gnepk” to the after-start peak engine speed target “tnepk” is inthe target range (KRNEPK2 to KRNEPK1). If it is true, it can beconsidered that the burning state is good. Therefore, the programproceeds to step 1010 and returns.

On the other hand, when it is not true in step 1006, it can beconsidered that the burning state is bad. Therefore, the programproceeds to step 1007, and the flag “xnedwn” showing a bad burning stateis set at ON.

In step 1008, the value (command value) of the next time of a quantityof suction air is set at the value of the present time, that is, thequantity of suction air is not changed. In step 1009, the value of thenext time of ignition timing is found when the present time value ofignition timing is multiplied by the ratio “rnepk”=“tnepk”/“gnepk”, andthe program proceeds to step 1010 and returns.

FIGS. 2(A) and 2(B) are views for explaining a judgment of the burningstate of the first embodiment. FIG. 2(A) is a view showing a case inwhich the after-start peak engine speed actual value “gnepk” is muchlower than the after-start peak engine speed target value “tnepk” due toa bad burning state, and the ratio “rnepk”=“tnepk”/“gnepk” is higherthan the upper limit KRNEPK2 of the target range. On the other hand,FIG. 2(B) is a view showing a case in which the burning state is goodand the after-start peak engine speed actual value “gnepk” isapproximately the same as the after-start peak engine speed target value“tnepk”, and the ratio “rnepk”=“tnepk”/“gnepk” is in the target range.

In the first variation of the first embodiment, when bad burning occursafter the start of the engine of the present time, the quantity ofsuction air of the next start of the engine is made to be the same asthat of the quantity of suction air of the present start of the engineas described above. Instead of that, the ignition timing is changed. Asa result, after the start of the engine of the next time, deteriorationof the burning state, which is caused by a change in the quantity ofsuction air, does not occur. As a result of the change in the ignitiontiming, the ratio “rnepk”=“tnepk”/“gnepk” of the after-start peak enginespeed actual value “gnepk” to the after-start peak engine speed targetvalue “tnepk” can be in the target range.

First Variation of the First Embodiment

The first variation of the first embodiment is operated as follows. Eachrate of change of the engine speed in each minute period in apredetermined period after the start of the engine is detected. When athus detected value is out of a predetermined target range, it is judgedthat a bad burning state has occurred, and the value of the present timeof ignition timing (command) is corrected so that each rate of change ofthe engine speed in each minute period in a predetermined period afterthe start of the engine can be in the target range, and the thuscorrected value is set as the value of the next time. The quantity ofsuction air (command value) of the present time is used for the nexttime, as it is.

However, the ignition timing of the next time is found by adding apredetermined correction value to the ignition timing of the presenttime.

FIG. 3 is a flow chart in which control of the first variation of thefirst embodiment is conducted. Since the steps 1101 and 1102 are thesame as those of the first embodiment, the explanations will be omittedhere.

In step 1103, the rate of change “gdlne” of the engine speed in eachminute period is calculated. In step 1104, it is judged whether or notthe rate of change “gdlne” of the engine speed in each minute period,which has been calculated in step 1103, is in the target range (KDLNE2to KDLNE1). If it is true, the burning state can be considered to begood. Therefore, the program proceeds to step 1111 as it is and returns.

On the other hand, if it is not true in step 1104, the burning state canbe considered to be bad. Therefore, program proceeds to step 1105, andthe flag “xnedwn”, which expresses a bad burning state, is set at ON.

In step 1106, the quantity of suction air of the next time is made to bethe same as the value of the present time, that is, a change in thequantity of suction air is prohibited.

In step 1107, it is judged whether or not the rate of change “gdlne” ofthe engine speed exceeds an upper limit. If it is true, that is, if therate of change “gdlne” of the engine speed exceeds an upper limit, theafter-start engine speed change rate “gdlne” of the present time issuddenly increased exceeding the upper limit KDLNE2 of the target value.Therefore, in step 1108, the correction value ΔIA is subtracted from theignition timing IAST of the present time, so that the spark timing isdelayed so as to decrease the engine speed. Then, the program proceedsto step 1111 and returns.

On the other hand, when it is not true in step 1107, the programproceeds to step 1109, and it is judged whether or not the rate ofchange “gdlne” of the engine speed is lower than the lower limit KDLNE1in the target range. It is true in step 1109 when the after-start enginespeed change rate “gdlne” of the present time is lower than the lowerlimit KDLNE1 of the target range and the engine speed is quicklydecreased. Therefore, in step 1110, the correction ΔIA is added to theignition timing IAST of the present time so that the spark timing can beadvanced so as to increase the engine speed. Then, the program proceedsto step 1111 and returns. In this connection, it is essentially couldnot be occurred to deny in step 1109. Therefore, the program proceeds tostep 1111 as it is and returns.

FIGS. 4(A) and 4(B) are views for explaining a judgment of the burningstate of the first variation of the first embodiment described above.FIG. 4(A) shows a case in which the after-start engine speed decreasesdue to bad burning, so that the engine speed change rate “gdlne” becomeslower than the lower limit KDLNE1 of the target range. On the otherhand, FIG. 4(B) shows a case in which the burning state is good and theengine speed change rate “gdlne” is in the target range.

As described above, in the first variation of the first embodiment, anoperation is conducted as follows. In the case where bad burning occursafter the start of the engine of the present time, the quantity ofsuction air of the start of the engine of the next time is made to bethe same as that of the present time. Instead of that, the ignitiontiming of the next time is changed. As a result, after the start of theengine of the next time, no deterioration is caused in the burning stateby the change in the quantity of suction air, and the engine speedchange rate “gdlne” in a minute period can be in the target range by theeffect of changing the ignition timing.

In this connection, in the case of the first embodiment in which thepeak engine speed is made to be the index to be controlled, it ispossible to conduct an operation like the first variation in such amanner that the correction ΔIA is added to or subtracted from theignition timing IAST of the present time so that it can be the ignitiontiming IAST of the next time.

Second Variation of the First Embodiment

Operation of the second variation of the first embodiment is conductedas follows. An average value of the engine speed change rate of in theminute period in the predetermined period after the start of the engineis learned (stored and renewed). In the case where a ratio of thislearning value to the target value (stored in ECU 10), which ispreviously determined corresponding to the engine temperature, is out ofthe predetermined target range, it is judged that a bad burning statehas occurred. Therefore, the ignition timing (command) of the presenttime is corrected so that this ratio can be in the target range in thenext time. The thus obtained ignition timing is set to be the value ofthe next time. The quantity of suction air (command) of the present timeis used for the value of the next time as it is.

FIG. 5 is a flow chart used for controlling the second embodiment. Steps1201 to 1203 in the second embodiment are the same as steps 1101 to 1103of the first variation. Therefore, the explanations will be omittedhere.

In step 1204, the after-start engine speed change rate mean actual value“gdlnesm” is calculated. In this case, the after-start engine speedchange rate mean actual value “gdlnesm” is obtained when the enginespeed change rates in the minute periods in the predetermined periodsare averaged. In this case, the average is not limited to a simple meanbut may also be a weighted mean by which an appropriate judgment can bemade.

Next, in step 1205, the after-start engine speed change rate averagetarget value “tdlnesm” is read in from the map. In step 1206, the ratio“rdlnesm”=“tdlnesm”/“gdlnesm” of the after-start engine speed changerate average actual value “gdlnesm” to the after-start engine speedchange rate average target value “tdlnesm” is calculated.

In step 1207, it is judged whether or not the ratio “rdlnesm” found instep 1206 is in the target range (KRDLNESM2 to KRDLNESM1). When it isnot true in step 1207, the program proceeds to step 1211 and returns.When it is true, it means that the after-start engine speed change ratemean actual value “gdlnesm” is greatly different from the after-startengine speed change rate average target value “tdlnesm” and burning isin a bad state. Therefore, the flag “xnedwn” showing the occurrence ofbad burning is set at ON in step, 1208. In step. 1209, the quantity ofsuction air of the next time (command) is set at the quantity of suctionair of the present time as it is. In step 1210, the ignition timing ofthe next time is set at a value obtained when the value of the presenttime is multiplied by the ratio “rdlnesm”=“tdlnesm”/“gdlnesm” describedbefore. Then, the program process to step 1211 and returns.

In this connection, the engine speed change rate “gdlne” is calculatedin the same minute period as that of the first variation of the firstembodiment. However, it is possible to make the period longer so far thejudgment is not affected by the roughness of the period.

FIGS. 6(A) and 6(B) are views for explaining a judgment of the burningstate of the second variation of the first embodiment. FIG. 6(A) shows acase in which the after-start engine speed decreases due to bad burning.As a result, FIG. 6(A) shows that the engine speed is decreased due tobad burning and the ratio “rdlnesm”=“tdlnesm”/“gdlnesm” of theafter-start engine speed change rate average actual value “gdlnesm” ofthe next time to the after-start engine speed change rate average targetvalue “tdlnesm” exceeds the upper limit KRDLNESM2 of the target range.On the other hand, FIG. 6(B) shows that the burning state is good andthe ratio “rdlnesm”=“tdlnesm”/“gdlnesm” is in the target range.

As described above, in the second variation of the first embodiment, theoperation is conducted as follows. In the case where bad burning occursafter the start of the engine of the present time, the quantity ofsuction air of the start of the engine of the next time is made to bethe same as that of the present time. Instead of that, the ignitiontiming of the next time is changed. As a result, after the start of theengine of the next time, no deterioration is caused in the burning stateby the change in the quantity of suction air. By the effect of thechange in the ignition timing, the ratio “rdlnesm”=“tdlnesm”/“gdlnesm”of the after-start engine speed change rate average actual value“gdlnesm” to the after-start engine speed change rate average targetvalue “tdlnesm” is put into the target range.

In this connection, concerning the second variation, it is possible toconduct an operation like the first variation in such a manner that thecorrection ΔIA is added to or subtracted from the ignition timing IASTof the present time so that it can be the ignition timing IAST of thenext time.

Second Embodiment

In the second embodiment, the operation is conducted as follows. Thepeak engine speed in a predetermined period after the start of theengine is learned (stored and renewed). When a ratio of this learningvalue to the target value (stored in ECU 10), which has been previouslydetermined corresponding to the engine temperature, is out of the targetrange which has been previously determined, it is judged that theburning state is bad. Therefore, the quantity of fuel injection(command) of the present time is corrected and made to be the value ofthe next time so that the ratio can be in the target range after thestart of the engine in the next time. The quantity of suction air(command) of the present time is used for the quantity of suction air ofthe next time as it is.

FIG. 7 is a flow chart for conducting control of the second embodiment.Steps 2001 to 2008 and step 2010 of this flow chart are the same assteps 1001 to 1008 and step 1010 in the first embodiment. However, onlystep 2009 is different, that is, the quantity of fuel injection ischanged, instead of the injection timing, in step 2009. In step 2009,the quantity of fuel injection (command) TAUST of the next time isdetermined in such a manner that the value TAUST of the present time ismultiplied by the ratio “rnepk”=“tnepk”/“gnepk” of the after-start peakengine speed actual value “gnepk” to the after-start peak engine speedtarget value “tnepk”.

In the second embodiment, when bad burning occurs after the start of theengine of the present time, the quantity of suction air of the nextstart of the engine is made to be the same as that the quantity ofsuction air of the present start of the engine as described above.Instead of that, ignition timing is changed. As a result, after thestart of the engine of the next time, deterioration of the burningstate, which is caused by a change in the quantity of suction air, doesnot occur. As a result of the change in the quantity of fuel injection,the ratio “rnepk”=“tnepk”/“gnepk” of the after-start peak engine speedactual value “gnepk” to the after-start peak engine speed target value“tnepk” can be in the target range.

In this connection, in this second embodiment, the quantity of fuelinjection (command) TAUST of the next time is determined in such amanner that the value TAUST of the present time is multiplied by theratio “rnepk”=“tnepk”/“gnepk” of the after-start peak engine speedactual value “gnepk” to the after-start peak engine speed target value“tnepk”. However, like the first variation of the first embodiment, itis possible to determined the quantity of fuel injection TAUST of thenext time in such a manner that the correction ΔTAU is added to orsubtracted from the quantity of fuel injection TAUST of the present timecorresponding to the value of “tnepk”/“gnepk”.

Concerning the index to be controlled, it is Possible to use theafter-start engine speed change ratio instead of the peak engine speedas the first variation of the first embodiment, and also it is possibleto use the after-start engine speed change ratio mean value as thesecond variation of the first embodiment.

Third Embodiment>

In the third embodiment, the operation is conducted as follows. The peakengine speed in a predetermined period after the start of the engine islearned (stored and renewed). When a ratio of this learning value to thetarget value (stored in ECU 10), which has been previously determinedcorresponding to the engine temperature, is out of the target rangewhich has been previously determined, it is judged that the burningstate is bad. Therefore, the quantity of fuel injection (command) of thepresent time is corrected and made to be the value of the next time sothat the ratio can be in the target range after the start of the enginethe next time. The quantity of suction air (command) of the present timeis used for the quantity of suction air of the next time, as it is.

FIG. 8 is a flow chart for conducting control of the third embodiment.Steps 3001 to 3008 and step 3010 of this flow chart are the same assteps 1001 to 1008 and step 1010 in the first embodiment. However, onlystep 3009 is different, that is, the fuel injection timing is changedinstead of the ignition timing. In step 3009, the fuel injection timingof the next time (command) INJST is determined from a map according tothe ratio “rnepk” of the after-start engine speed peak actual value“gnepk” to the after-start engine speed peak target value “tnepk”.

FIG. 9 is the map described above. The horizontal axis represents theratio “rnepk”=“tnepk”/“gnepk” of the after-start engine speed peakactual value “gnepk” to the after-start engine speed peak target value“tnepk”, and the vertical axis represents INJST, that is, specifically,the vertical axis represents the time of completion of injection.According to the value of “rnepk”=“tnepk”/“gnepk”, fuel injection can beclassified into non-synchronous injection and synchronous injection. Innon-synchronous injection, injection is conducted before the suctionvalve is opened. In synchronous injection, injection is conducted whilethe suction valve is being opened. When non-synchronous injection isconducted in a cold state of the engine, drips of fuel stay on thereverse side of the suction valve, which could be a cause of badburning. On the other hand, when synchronous injection is conducted innormal operation of the engine, the atomizing time becomes so short thatthe burning state is deteriorated.

In the third embodiment, when bad burning occurs after the start of theengine of the present time, the quantity of suction air of the nextstart of the engine is made to be the same as that the quantity ofsuction air of the present start of the engine as described above.Instead of that, the fuel injection timing is changed. As a result,after the start of the engine of the next time, deterioration of theburning state, which is caused by a change in the quantity of suctionair, does not occur. As a result of the change in fuel injection timing,the ratio “rnepk”=“tnepk”/“gnepk” of the after-start peak engine speedactual value “gnepk” to the after-start peak engine speed target value“tnepk” can be in the target range.

Concerning the index to be controlled, it is possible to use theafter-start engine speed change ratio instead of the peak engine speedas the first variation of the first embodiment, and also it is possibleto use the after-start engine speed change ratio mean value as thesecond variation of the first embodiment.

Fourth Embodiment

In the fourth embodiment, the operation is conducted as follows. Theengine speed change rate in the minute period in the predeterminedperiod after the start of the engine is detected. In the case where thusdetected value is out of the target range, it is judged that a badburning state has been caused. At the same time, a cylinder in which badburning has occurred is discriminated. The ignition timing (command) ofthe cylinder, in which bad burning has occurred, of the present time iscorrected so as to obtain the ignition timing of the next time so thatthe engine speed change rate in the minute period in the predeterminedperiod after the start of the engine of the next time can not out of thejudgment value, that is, the engine speed change rate in the minuteperiod in the predetermined period after the start of the engine of thenext time can exceed the judgment value. Concerning the quantity ofsuction air (command), the value of the present time is used for thevalue of the next time as it is.

The reason why the engine speed change rate in the minute period is usedfor the index to be controlled is that the engine speed change rate inthe minute period is appropriate for judging a cylinder compared withthe peak engine speed and the engine speed change rate average becausethe detection interval is short.

FIG. 10 is a flow chart for controlling the fourth embodiment. This flowchart is composed as follows. After step 1106 in the flow chart of thefirst variation of the first embodiment, a step to discriminate acylinder is inserted, and the ignition timing of only the cylinder in abad burning state is corrected in steps 4009 and 4011 corresponding tosteps 1108 and 1010 in the flow chart of the first variation of thefirst embodiment.

As described before, this cylinder discrimination is conducted asfollows. Time (angle) from the reference signal generated by the camposition sensor 30 is measured on the basis of the signal generated bythe crank position sensor 21.

In the fourth embodiment, as described before, when bad burning occursafter the start of the engine of the present time, the quantity ofsuction air of the next start of the engine is made to be the same asthat the quantity of suction air of the present start of the engine.Instead of that, the ignition timing is changed. As a result, after thestart of the engine of the next time, deterioration of the burningstate, which is caused by a change in the quantity of suction air, doesnot occur. As a result of the change in the ignition timing, the enginespeed change rate “gdlne” in the minute period can be put into thetarget range. In this case, a cylinder in a bad burning state isspecified, and the ignition timing of only that cylinder is changed, andthe ignition timing of other cylinders, the change of ignition timing ofwhich is unnecessary, is not changed. Therefore, it is possible toprevent the deterioration of exhaust gas and drivability caused bytaking a redundant countermeasure.

In this connection, concerning the index to be controlled, instead ofthe ignition timing, it is possible to use the quantity of fuelinjection like the second embodiment, and it is also possible to use thefuel injection timing as in the third embodiment. Concerning the methodof correction, the value of the present time may be multiplied by aratio so as to obtain the value of the next time.

Embodiments of the Second Group

Next, the embodiment of the second group will be explained below. Thisembodiment of the second group is an idling engine speed control unit bywhich the engine speed in the idling steady state is controlled so thatit can reach a target value. In this case, the idling steady state is anidling state from which the engine speed increasing state and thecoasting state are excluded.

Therefore, in the idling engine speed control unit of the embodiment ofthe second group, a bad burning state, which occurs when the idlingengine speed is subjected to feedback control of the quantity of suctionair, is positively detected and control is changed over so that it canbe conducted by another control parameter.

In this connection, in the initial state, the idling engine speed iscontrolled by the feedback control of the quantity of suction air.

Fifth Embodiment

In this embodiment, when it is judged that a bad burning state hasoccurred in feedback control of the quantity of suction air to controlthe idling engine speed, control is changed over to the idling enginespeed control conducted by another control parameter. Especially whenthe burning state is bad although the idling engine speed is subjectedto feedback control of the quantity of suction air and feedback controlof the air/fuel ratio is not executed, control is changed over tofeedback control of the ignition timing.

FIG. 11 is a flow chart of the fifth embodiment. In step 5001, it isjudged whether or not it is in an idling state. This judgment isconducted by the signal of the throttle opening degree sensor 4 or theaccelerator opening degree sensor 15 and by the signal of the vehiclespeed sensor 31. In step 5002, it is judged whether or not feedbackcontrol of the air/fuel ratio of the engine 1 is executed.

When it is not true in steps 5001 and 5002, the program proceeds to step5010. When it is true in both steps 5001 and 5002, the program proceedsto step 5003, and it is judged whether or not the burning state is bad.

This judgment to judge whether or not the burning state is bad isconducted by what is the most appropriate for the idling speed controlmethod executed at that time. For example, since feedback control of thequantity of suction air is executed at first, it is judged by whether ornot a change in the engine speed with respect to the change in thethrottle opening degree in feedback control of the quantity of suctionair is in a predetermined region. FIG. 24 is a view to explain thisjudgment.

When it is true in step 5003 that the burning state is bad, the programproceeds to step 5004, and the bad burning state flag “xnedwn” is set ONand the program proceeds to step 5005. On the other hand, when it is nottrue in step 5003, the program proceeds to step 5009, and the badburning state flag “xnedwn” is set OFF and the program proceeds to step5010.

In step 5005, the suction air quantity feedback control execution flag“xqfb” is set OFF, and the ignition timing feedback control flag.“xiafb” is set ON. In step 5006, engine speed deviation “dlne” betweenthe target engine speed “tne” and the actual engine speed “ne” is found.In step 5007, the ignition timing correction “dlmia” corresponding toengine speed deviation “dlne” is found from the map in FIG. 21. In step.5008, the ignition timing correction “dlmia” calculated in step 5007 isadded to the ignition timing “ia” of the present time so that theignition timing “ia” of the next time is calculated. Then, the programproceeds to step 5011 and returns. On the other hand, when the programproceeds to step 5010, the suction air quantity feedback controlexecution flag “xqfb” is set at “ON” in step 5010, and the ignitiontiming feedback control flag “xiafb” is set at OFF. Then, the programproceeds to step 5011 and returns.

Since the first embodiment operates as described above, if the burningstate is bad in suction air quantity feedback control, ignition timingfeedback control is conducted.

In this connection, in the case where the program returns via step 5008,it is in the state of ignition timing feedback control. Therefore, thejudgment to judge whether or not the burning state is bad, which isconducted in step 5003, is conducted by a method appropriate for thisignition timing feedback control. The method can be the same as that ofthe judgment conducted in suction air quantity feedback control, thatis, it can be judged by whether or not engine speed fluctuation “dlne”with respect to ignition timing fluctuation “dlia” in ignition timingfeedback control is in a predetermined region. Also, it is possible tojudge by whether or, not engine speed deviation “dlne” is larger thanthe predetermined judgment value KDLNEA.

As described above, the judgment to judge whether or not the burningstate is bad in step 5003, conducted after the program has returned, isconducted by a method appropriate for the control method executed atthat time, which is the same in each embodiment described later.

First Variation of the Fifth Embodiment

In this variation, the operation is conducted as follows. When theidling engine speed is subjected to suction air quantity feedbackcontrol and the burning state is bad and when air/fuel ratio feedbackcontrol is not executed, control is changed over to fuel injectionquantity feedback control.

FIG. 12 is a flow chart of the first variation of the fifth embodiment.Step 5101 is the same as step 5001 in the fifth embodiment.

In step 5102, whether or not the engine temperature is lower than thepredetermined temperature, that is, whether or not the engine is in anidling state is judged by whether or not the coolant temperature “tw”detected by the coolant temperature sensor 11 is lower than thepredetermined value KTW1. When it is not true in steps 5101 and 5102,the program proceeds to step 5110. Only when it is true in both steps5101 and 51Q2, does the program proceed to step 5103.

Steps 5103, 5104 and 5109 are the same as steps 5003, 5004 and 5009 inthe first embodiment. Therefore, the explanations of those steps areomitted here.

In step 5105, the suction air quantity feedback control execution flag“xqfb” is set OFF, and the fuel injection quantity feedback control flag“xtaufb” is set ON. In steps 5106, 5107, the fuel injection quantitycorrection “dlmtau” corresponding to engine speed deviation “dlne” isfound from the map in FIG. 22. In step 5108, the fuel injection quantitycorrection “dlmtau” calculated in step 5107 is added to the fuelinjection quantity “tau” of the present time, so that the fuel injectionquantity “tau” of the next time is calculated. Then, the programproceeds to step 5111 and returns.

On the other hand, in the case where the program proceeds to step 5100,the suction air quantity feedback control execution flag “xqfb” is setat ON in step 5110, and the fuel injection quantity feedback controlflag “xtaufb” is set at OFF. Then, the program proceeds to step 5111 andreturns.

The first variation of the first embodiment operates as described above.Therefore, when the burning state is bad in suction air quantityfeedback control, fuel injection quantity feedback control is conducted.

Second Variation of the Fifth Embodiment

In this second variation of the fifth embodiment, when the burning stateis bad even if the idling engine speed is subjected to suction airquantity feedback control and when a predetermined period of time hasnot passed after the start of the engine, control is changed over tofuel injection timing control.

FIG. 13 is a flow chart of the second variation of the fifth embodiment.Step 5201 is the same as step 5001 in the fifth embodiment.

In step 5202, whether or not the elapse time after the start of theengine is longer than a predetermined period of time is judged by thetimer in ECU 10.

In the case where it is not true in steps 5201 and 5202, the programproceeds to step 5210. Only when it is true in both steps 5201 and 5202,the program proceeds to step 5203.

Steps 5203, 5204 and 5209 are the same as steps 5003, 5004 and 5009 inthe fifth embodiment. Therefore, the explanations of those steps areomitted here.

In step 5205, the suction air quantity feedback control execution flag“xqfb” is set at OFF, and the fuel injection timing control flag“xinjtc” is set at ON. In step 5206, the ratio “r”=“tne”/“ne” of thetarget engine speed “tne” to the actual engine speed “ne” is calculated.In step 5207, fuel injection timing “minj” corresponding to the ratio“r”=“tne”/“ne” calculated in step 5206 is found from the map in FIG. 23.In step 5208, fuel injection timing “minj” calculated in step 5207 isused as fuel injection timing “inj” of the next time, and the programproceeds to step 5211 and returns.

On the other hand, in the case where the program proceeds to step 5210,the suction air quantity feedback control execution flag “xqfb” is setat ON in step 5210, and the fuel injection timing control flag “xinjtc”is set at OFF. Then, the program proceeds to step 5211 and returns.

The second variation of the fifth embodiment operates as describedabove. Therefore, when the burning state is bad in suction air quantityfeedback control, fuel injection timing feedback control is conducted.

Sixth Embodiment

The sixth embodiment operates as follows. When it is judged that theburning state is bad by suction air quantity feedback control of theengine speed, the suction air quantity feedback control is stopped, andcontrol is conducted by another control parameter. After that, suctionair quantity feedback control is conducted again. In the above state,the burning state is rejudged. When the burning state is bad, suctionair quantity feedback control is stopped and control is conducted byanother control parameter.

Especially when the burning state is bad in suction air quantityfeedback control, the suction air quantity feedback control is stopped,and the ignition timing is advanced by a predetermined angle. Afterthat, control is returned to suction air quantity feedback control. Whenthe burning state is bad, the suction air quantity feedback control isstopped, and the ignition timing is further advanced by a predeterminedangle. In this case, the spark advance is limited by the guard value.

FIG. 14 is a flow chart of the sixth embodiment. Steps 6001 and 6002 arethe same as steps 5001 and 5002 in the first embodiment.

In the case where it is not true in step 6001 or 6002, the programproceeds to step 6012. Only when it is true in both steps 6001 and 6002,the program proceeds to step 6003.

Steps 6003, 6004 and 6011 are the same as steps 5003, 5004 and 5009 inthe fifth embodiment. Therefore, the explanations of those steps areomitted here.

In step 6005, the suction air quantity feedback control execution flag“xqfb” is set at OFF, and the ignition timing quantitative advance angleflag “xiaadd” is set at ON. Then the program proceeds to step 6006, andit is judged whether or not ignition timing “ia” is not more than theupper limit guard value KIA.

When it is not true in step 6006, the program proceeds to step 6010, andignition timing “ia” is fixed at the guard value. Then, the programproceeds to step 6013 and returns. On the other hand, in the case whereit is true in step 6006, ignition timing “ia” is advanced by apredetermined value in step 6007, for example, ignition timing “ia” isadvanced by ΔA in step 6007, and then the program proceeds to step 6008and the suction air quantity feedback control execution flag “xqfb” isset at ON and the ignition timing quantitative advance angle flag“xiaadd” is set at OFF. Due to the foregoing, suction air quantityfeedback control is executed again. Therefore, it is judged in step 6009whether or not the burning state is bad. In the case where it is nottrue in step 6009, the program proceeds to step 6013 and returns. In thecase where it is not true in step 6009, steps after step 6005 arerepeated.

On the other hand, in the case of proceeding to step 6012, the suctionair quantity feedback control execution flag “xqfb” is set at ON and theignition timing quantitative advance angle flag “xiaadd” is set at OFF.Then, the program proceeds to step 6013 and returns.

Since the sixth embodiment operates as described above, when the burningstate is bad in suction air quantity feedback control, suction airquantity feedback control is stopped and ignition timing is advanced bya predetermined angle. After that, control is returned to suction airquantity feedback control, and when the burning state is bad, suctionair quantity feedback control is stopped, and ignition timing is furtheradvanced by a predetermined angle.

Variation of the Sixth Embodiment

This variation operates as follows. When the burning state is bad insuction air quantity feedback control, suction air quantity feedbackcontrol is stopped, and the fuel injection quantity is increased by apredetermined value. After that, control is returned to suction airquantity feedback control, and when the burning state is bad, thesuction air quantity feedback control is stopped and the fuel injectionquantity is further increased by a predetermined value. In this case,the increase is limited by the guard value.

FIG. 15 is a flow chart of the variation of the sixth embodiment. Inthis flow chart shown in FIG. 15, the ignition timing in the flow chartof the sixth embodiment is replaced with the fuel injection quantity.Therefore, the detailed explanation will be omitted here.

Seventh Embodiment

The seventh embodiment operates as follows. When it is judged by suctionair quantity feedback control of the idling engine speed that theburning state is bad, control is carried out by another controlparameter. After that, suction air quantity feedback control isconducted again, and when the burning state is bad in this state,control is further conducted by still another control parameter. Whenthe burning state is bad in suction air quantity feedback control, thesuction air quantity feedback control is stopped, and fuel injectiontiming is set at the fuel injection timing of non-synchronous injection.After that, control is returned to suction air quantity feedbackcontrol. When the burning state is bad, the suction air quantityfeedback control is stopped, and ignition timing is advanced by apredetermined value. In this case, the advance value is limited by theguard value.

In this case, the reason why fuel injection timing control is executedfirst and ignition timing quantitative advance angle control is executednext is described as follows. Since fuel injection timing control hasless influence on exhaust gas emission than ignition timing quantitativeadvance angle control, first, control is conducted by the fuel injectiontiming control having less influence on exhaust gas emission, and whenthe burning state is bad even if fuel injection timing control isexecuted, ignition timing quantitative advance angle control having moreinfluence on exhaust gas emission is executed, so that the deteriorationof exhaust gas emission can be reduced to as small as possible.

In this connection, the influence given to exhaust gas emission isincreased in the order of control of the suction air quantity, controlof fuel injection timing, control of ignition timing and control of thefuel injection quantity.

FIGS. 16 and 17 are views showing a flow chart of the seventhembodiment. Steps 7001 and 7002 in this flow chart are the same as steps5001 and 5002 in the fifth embodiment.

When it is not true in steps 7001 or 7002, the program proceeds to step7017. Only when it is true in both steps 7001 and 7002, the programproceeds to step 7003.

Since steps 7003, 7004 and 7016 are the same as steps 5003, 5004 and5009 in the fifth embodiment, the explanations are omitted here.

In step 7005, the suction air quantity feedback control execution flag“xqfb” is set OFF, and the fuel injection timing control flag “xinjtc”is set ON, and the ignition timing quantitative advance angle flag“xiaadd” is set OFF and the program proceeds to step 7006 and it isjudged whether or not the fuel injection timing is set at the injectiontiming of synchronous injection.

When it is not true in step 7006, the program proceeds to step 7007, andthe fuel injection timing is set at the injection timing of synchronousinjection. Then, the program proceeds to step 7008, and the suction airquantity feedback control execution flag “xqfb” is set ON, and the fuelinjection timing control flag “xinjtc” is set OFF, and the ignitiontiming quantitative advance angle flag “xiaadd” is set OFF. Due to theforegoing, suction air quantity feedback control is executed again.Therefore, it is judged whether or not the burning state is bad in step7009. When it is true in step 7009, the program proceeds to step 7018and returns.

On the other hand, when it is true in step 7006 and when it is true instep 7009, the program proceeds to step 7010 and the suction airquantity feedback control execution flag “xqfb” is set OFF, and the fuelinjection timing control flag “xinjtc” is set OFF, and the ignitiontiming quantitative advance angle flag “xiaadd” is set ON. Then, theprogram proceeds to step 7011.

In step 7011, it is judged whether or not the ignition timing is lowerthan the predetermined guard value KIA. When it is true in step 7011,the ignition timing “ia” is advanced by a predetermined advance angle,for example, the ignition timing “ia” is advanced by ΔA in step 7012.Then, the program proceeds to step 7013, and the suction air quantityfeedback control execution flag “xqfb” is set at ON, and the fuelinjection timing control flag “xinjtc” is set at OFF, and the ignitiontiming quantitative advance angle flag “xiaadd” is set at OFF. Due tothe foregoing, suction air quantity feedback control is executed again.Therefore, it is judged whether or not the burning state is bad in step7014.

When it is true in step 7014, steps after step 7010 are repeated. Whenit is not true in step 7014, the program proceeds to step 7018 andreturns. When it is not true instep 7011, the ignition timing “ia” isfixed at the guard value KIA in step 7015, and then the program proceedsto step 7018 and returns.

On the other hand, when the program proceeds to step 7017, the suctionair quantity feedback control execution flag “xqfb” is set at ON, andthe ignition timing quantitative advance angle flag “xiaadd” is set atOFF, and the program proceeds to step 7018 and returns.

Since the seventh embodiment operates as described above, when theburning state is bad in suction air quantity feedback control, suctionair quantity feedback control is stopped and the fuel injection timingis set at the timing of non-synchronous injection. After that, controlis returned to suction air quantity feedback control. When the burningstate is bad even after that, suction air quantity feedback control isstopped, and ignition timing quantitative advance angle control isexecuted.

Variation of the Seventh Embodiment

The variation of the seventh embodiment operates as follows. When theburning state is bad in suction air quantity feedback control, suctionair quantity feedback control is stopped, and the ignition timing isadvanced by a predetermined angle. After that, control is returned tosuction air quantity feedback control. When the burning state is badeven after that, suction air quantity feedback control is stopped, andthe quantity of fuel injection is increased by a predetermined value. Inthis case, the advance angle is limited to the guard value, and also thevalue of increase in fuel injection is limited to the guard value.

In this case, the reason why ignition timing control is executed firstand fuel injection quantity control is executed next is described asfollows. Since ignition timing control has less influence on exhaust gasemission than fuel injection quantity control, first, control isconducted by the ignition timing control having less influence onexhaust gas emission in the same manner as that of the third embodiment,and when the burning state is bad even if ignition timing control isexecuted, fuel injection quantity control having more influence onexhaust gas emission is executed, so that the deterioration of exhaustgas emission can be reduced as small as possible.

FIGS. 18 and 19 are views showing a flow chart of the variation of theseventh embodiment. Steps 7101 and 7102 in this flow chart are the sameas steps 7001 and 7002 in the seventh embodiment.

When it is not true in steps 7101 or 7102, the program proceeds to step7118. Only when it is true in both steps 7101 and 7102, does the programproceed to step 7103.

Since steps 7103, 7104 and 7117 are the same as steps 7003, 7004 and7016 in the third embodiment, the explanations are omitted here.

In step 7105, the suction air quantity feedback control execution flag“xgfb” is set at OFF, and the ignition timing quantitative advance angleflag “xiaadd” is set at ON, and the fuel injection quantitative increaseflag “xtauadd” is set at OFF, and the program proceeds to step 7106, andit is judged whether or not the ignition timing is lower than thepredetermined guard value KIA. When it is true in step 7106, theignition timing “ia” is advanced by a predetermined angle in step 7107,for example, the ignition timing “ia” is advanced by ΔA, and then theprogram proceeds to step 7108, and the suction air quantity feedbackcontrol execution flag “xgfb” is set at “ON” and the ignition timingquantitative advance angle flag “xiaadd” is set at OFF, and the fuelinjection quantitative increase flag “xtauadd” is set at OFF. Due to theforegoing, suction air quantity feedback control is executed again.Therefore, it is judged in step 7109 whether or not the burning state isbad. When it is not true in step 7109, the program proceeds to step 7119and returns.

On the other hand, when it is not true in step 7106 and when it is truein step 7109, the program proceeds to step 7111 and the suction airquantity feedback control execution flag “xgfb” is set OFF, and theignition timing quantitative advance angle flag “xiaadd” is set OFF, andthe fuel injection quantitative increase flag “xtauadd” is set ON. Then,the program proceeds to step 7112.

In step 7112, it is judged whether or not the fuel injection quantity“tau” is lower than the predetermined guard value KTAU.

When it is true in step 7112, the fuel injection quantity “tau” isincreased in step 7113 by a predetermined correction quantity, forexample, the fuel injection quantity “tau” is increased in step 7113 byΔB. Then, the program proceeds to step 7114, and the suction airquantity feedback control execution flag “xqfb” is set at ON, and theignition timing quantitative advance angle flag “xiaadd” is set at OFF,and the fuel injection quantitative increase flag “xtauadd” is set atOFF. Due to the foregoing, suction air quantity feedback control isexecuted again. Therefore, it is judged in step 7115 whether or not theburning state is bad. When it is true in step 7115, steps after step7111 are repeated, and when it is not true, the program proceeds to step7119 and returns. When it is not true in step 7112, the fuel injectionquantity “tau” is fixed at the guard value KTAU in step 7116, and thenthe program proceeds to step 7119 and returns.

On the other hand, when the program proceeds to step 7118, the suctionair quantity feedback control execution flag “xqfb” is set at ON, andthe ignition timing quantitative advance angle flat “xiaadd” is set atOFF, and then the program proceeds to step 7118 and returns.

Since the variation of the seventh embodiment operates as describedabove, when the burning state is bad in suction air quantity feedbackcontrol, suction air quantity feedback control is stopped and theignition timing is advanced by a predetermined angle. After that,control is returned to suction air quantity feedback control. When theburning state is bad even after that, suction air quantity feedbackcontrol is stopped, and fuel injection quantitative increase control isexecuted.

Eight Embodiment

In the eighth embodiment, when it is judged in suction air quantityfeedback control that the burning state is bad, control is executed byanother control parameter. In this case, a cylinder, the burning stateof which is bad, is discriminated, and control is executed by anothercontrol parameter. When the idling engine speed is subjected to suctionair quantity feedback control and the burning state is bad and theair/fuel ratio feedback control is not executed, control is changed toignition timing feedback control.

FIG. 20 is a flow chart to conduct controlling of the eighth embodiment.In this flow chart, after step 5004 of the fifth embodiment, the step todiscriminate a cylinder is inserted, and the ignition timing of acylinder, the burning state of which is bad, is corrected in steps 8006,8008, 8009 corresponding to steps 5005, 5007, 5008 in the flow chart ofthe fifth embodiment.

As described before, this discrimination of a cylinder, the burningstate of which is bad, is conducted by measuring a period of time(angle) from a reference signal generated by the cam position sensor 30on the basis of the signal of the crank position sensor 21.

As described above, in the eighth embodiment, in the case where theburning state is bad in suction air quantity feedback control, thecylinder, the burning state of which is bad, is specified, and ignitiontiming feedback control is conducted only on this cylinder, and ignitiontiming feedback control is not conducted on other cylinders for whichignition timing feedback control is unnecessary. Therefore, thedeterioration caused by exhaust gas and the deterioration ofdrivability, which are caused by a redundant countermeasure, can beprevented. In this connection, the above method in which the cylinder,the burning state of which is bad in suction air quantity feedbackcontrol, is specified and another control is conducted only on thecylinder, the burning state of which is bad, can be applied to not onlythe fifth embodiment but also other embodiments.

Embodiments of the Third Group

Embodiments of the third group will be explained below. This embodimentis an engine speed control unit characterized as follows. In theembodiments of the third group, in the case where the burning state isbad while suction air quantity feedback control is being conducted and aload change is caused while feedback control conducted by the ignitiontiming or the fuel injection quantity is being executed, the enginespeed is controlled so that it can reach the target value.

Ninth Embodiment

In the ninth embodiment, a load change is relatively small, and thetarget engine speed is not changed, and the reference value of thecontrol parameter is changed.

As an example, there is shown a case in which a load change is caused bythe influence of a power steering device while feedback control by theignition timing is being conducted.

FIG. 25 is a flow chart of the ninth embodiment. In step 9001, it isjudged whether or not it is in an idling state. This judgment isconducted by the signal sent from the throttle opening degree sensor 4or the accelerator opening degree sensor 15 and also by the signal sentfrom the vehicle speed sensor 31. In step 9002, it is judged whether ornot the burning state is bad.

In this connection, the method of judging whether or not the burningstate is bad is not limited to a specific method. For example, whetheror not the burning state is bad can be judged by a rise of the enginespeed immediately after the start of the engine. Also, whether or notthe burning state is bad can be judged by a ratio of the change in asuction air quantity to the change in the engine speed in the idlingstate.

When it is not true in step 9001, both the suction air quantity feedbackcontrol flag “xqfb” and the ignition timing feedback control flag“xiafb” are set OFF in step 9006, and the program proceeds to step 9008and returned.

When it is not true in step 9002, the program proceeds to step 9007, andthe ignition timing feedback control flag. “xiafb” is set OFF in step9007, and ignition timing feedback control is stopped, and the suctionair quantity feedback control execution flag “xqfb” is set at ON so asto conduct suction air quantity feedback control, and then the programproceeds to step 9008 and returns.

When it is true in both steps 9001 and 9002, the program proceeds tostep 9003, and the suction air quantity feedback control flag “xqfb” isset at OFF so as to stop suction air quantity feedback control, and theignition timing feedback control flag “xiafb” is set at ON so as toconduct ignition timing feedback control. Then, the program proceeds tostep 9004, and it is judged whether or not a load of the power steeringdevice has been changed. When it is not true in step 9004, the programproceeds to step 9008 as it is and returns. The change in the load ofthe power steering device is detected by the power steering loaddetection means 32 shown in FIG. 43.

When it is true in step 9004, the program proceeds to step 9005, and theignition timing reference value “mia” is changed, and the programproceeds to step 9008 and returns.

In this connection, when the load change is very small and thecontrollability can be kept without changing the ignition timingreference value “mia”, step 9005 may be omitted.

Variation of the Ninth Embodiment

FIG. 26 is a flow chart of control conducted in the variation of theninth embodiment. This variation of the ninth embodiment is essentiallythe same as the ninth embodiment. Therefore, the explanations will beomitted here.

In this case, the ignition timing reference value “mia” and the fuelinjection quantity reference value “mtau” will be explained here. Theignition timing reference value “mia” and the fuel injection quantityreference value “mtau” are values previously stored on the map in ECU 10corresponding to the coolant temperature according to the results ofexperiments when ignition timing feedback control or fuel injectionquantity feedback control is conducted. In the case where the idlingengine speed does not coincide with the target value, the changecorrection is increased or decreased by this reference value so that thedifference can be compensated.

Accordingly, in the case where the load change is large, unless thereference value is shifted corresponding to it, the correction isincreased and it takes long time to conduct controlling. On the otherhand, when the load change is small, the change in the correction isalso small. Therefore, it is unnecessary to shift the reference value.In this connection, these reference values may be respectively storedaccording to the load. Alternatively, only the reference value in thenormal state may be stored and corrected by a predetermined value.

In this connection, the suction air quantity reference value is alsoprepared for suction air quantity feedback control executed in a goodburning state.

The ninth embodiment and its variation operate as described above.Therefore, when the burning state becomes bad in suction air quantityfeedback control and the power steering load is changed while ignitiontiming feedback control or fuel injection quantity feedback control isbeing conducted, the ignition timing reference value “mia” or the fuelinjection quantity reference value “tau” is changed and feedback controlcan be continued.

Tenth Embodiment

Next, the tenth embodiment will be explained below. In this tenthembodiment, a change in the load is detected, and the control referencevalue is changed according to the change in the load. As an example,there is shown a case in which the ignition timing reference value “mia”is changed according to the change in the load given to the powersteering device.

FIG. 27 is a flow chart of the tenth embodiment. Steps 10001 to 10003are the same as steps 9001 to 9003 of the first embodiment, and steps10006 to 10007 are the same as steps 9006 to 9007 of the ninthembodiment. Therefore, the explanations are omitted here.

In the case where the program proceeds to step 10004, a change of theload given to the power steering device is detected in step 10004. Instep 10005 the ignition timing reference value “mia” corresponding tothe change of the load given to the power steering device is calculated.Then, the program proceeds to step 10008 and returns.

The tenth embodiment operates as described above. Therefore, when theburning state becomes bad in the process of suction air quantityfeedback control and ignition timing feedback control is conducted, theignition timing reference value “mia” is changed corresponding to theload given to the power steering device and feedback control iscontinued. In this connection, concerning this tenth embodiment, as thevariation of the ninth embodiment, it is possible to devise a variationin which feedback control is conducted by the fuel injection quantity.However, the explanation will be omitted here.

Eleventh Embodiment

Next, the eleventh embodiment will be explained below. In this eleventhembodiment, when a load given to the engine is changed, the target value“tne” of the idling engine speed is changed. Explanations will be madeinto an example in which a load given to the engine by electricauxiliary machines, which is referred to as an electric loadhereinafter, is changed when ignition timing feedback control isconducted.

FIG. 28 is a flow chart of the eleventh embodiment. Steps 11001 to 11003are the same as steps 9001 to 9003 of the ninth embodiment, and steps11006, 11007 are the same as steps 9006 to 9007 of the ninth embodiment.Therefore, the explanations are omitted here. In this connection,whether or not the electric load is changed is judged by ECU 10according to signals sent the auxiliary machines.

After the program has proceeded to step 11004, it is judged whether ornot the electric load is changed in step 11004. When it is true, thetarget engine speed “tne” is changed in step 11005, and the programproceeds to step 11008 and returns. When it is not true in step 11004,the program proceeds to step 11008 as it is and returns.

Eleventh embodiment operates as described above. Therefore, when theburning state becomes bad in the process of suction air quantityfeedback control and ignition timing feedback control is conducted, thetarget engine speed “tne” is changed when the electric load is changed,and feedback control is continued. In this connection, concerning thiseleventh embodiment, as the variation of the ninth embodiment, it ispossible to devise a variation in which feedback control is conducted bythe fuel injection quantity. However, the explanation will be omittedhere.

Twelfth Embodiment

Next, the twelfth embodiment will be explained below. In this twelfthembodiment, when a load given to the engine is changed, the target value“tne” of the idling engine speed is changed and also the controlreference value corresponding to the target value is changed.Explanations will be made into an example in which an electric load ischanged when ignition timing feedback control is conducted.

FIG. 29 is a flow chart of the twelfth embodiment. Steps 12001 to 12003are the same as steps 9001 to 9003 of the first embodiment, and steps12007, 12008 are the same as steps 9006, 9007 of the first embodiment.Therefore, the explanations are omitted here.

After the program has proceeded to step 12004, it is judged whether ornot the electric load is changed in step 12004. When it is true, thetarget engine speed “tne” is changed in step 12005, and the ignitiontiming reference value “mia” is changed in step 12006, and then theprogram proceeds to step 12009 and returns. When it is not true in step12004, the program proceeds to step 12009 as it is and returns.

Twelfth embodiment operates as described above. Therefore, when theburning state becomes bad in the process of suction air quantityfeedback control and ignition timing feedback control is conducted, thetarget engine speed “tne” and the ignition timing reference value “mia”are changed when the electric load is changed, and feedback control iscontinued. In this connection, concerning this twelfth embodiment, likethe variation of the ninth embodiment, it is possible to devise avariation in which feedback control is conducted by the fuel injectionquantity. However, the explanation will be omitted here.

Thirteenth Embodiment

Next, the thirteenth embodiment will be explained below. In thisthirteenth embodiment, a change in the load is detected, and the targetengine speed and the control reference value are changed correspondingto this change in the load. As an example, there is shown a case inwhich the target engine speed “tne” and the ignition timing referencevalue “mia” are changed corresponding to a change in the electric load.

FIG. 30 is a flow chart of the thirteenth embodiment. Steps 13001 to13003 are the same as steps 9001 to 9003 of the ninth embodiment, andsteps 13007, 13008 are the same as steps 9006, 9007 of the firstembodiment. Therefore, the explanations are omitted here.

When the program proceeds to step 13004, a change in the electric loadis detected in step 13004. In step 13005, the target engine speed “tne”is calculated corresponding to the change in the electric load detectedin step 13004. In step 13006, the ignition timing reference value “mia”is calculated, and the program proceeds to step 13009 and returns.

Thirteenth embodiment operates as described above. Therefore, when theburning state becomes bad in the process of suction air quantityfeedback control and ignition timing feedback control is conducted, thetarget engine speed “tne” and the ignition timing reference value “mia”are changed when the electric load is changed, and feedback control iscontinued.

In this connection, concerning this thirteenth embodiment, like thevariation of the ninth embodiment, it is possible to think a variationin which feedback control is conducted by tho fuel injection quantity.However, the explanation will be omitted here.

Fourteenth Embodiment

Next, the fourteenth embodiment will be explained below. This fourteenthembodiment complies with a case in which a change in the load is large.In this embodiment, the target value of the idling engine speed isincreased and the reference value of a parameter of feedback control isshifted and further other parameters are quantitatively changed.

As an example, there is shown a case in which a shift position of thetransmission connected with the engine 1 is moved between the stoppingposition (P, N) and the running position (D, R, 4, 3, 2, L) whileignition timing feedback control is being conducted. This movement ofthe shift position of the transmission is judged by a signal sent fromthe shift position sensor 33.

FIG. 31 is a flow chart of the fourteenth embodiment. Steps 14001 to14003 are the same as steps 9001 to 9003 of the ninth embodiment, andsteps 14007, 14009 are the same as steps 9006, 9007 of the ninthembodiment. Therefore, the explanations are omitted here.

In step 14004, it is judged whether or not the shift position ischanged. When it is not true, the program proceeds to step 14010 as itis and returns. When it is true, the target engine speed “tne” ischanged in step 14005. In step 14006, the ignition timing referencevalue “mia” is changed. In step 14007, the fuel injection quantity ischanged by a predetermined value, and the program proceeds to step 14010and returns.

The fourteenth embodiment operates as described above. Therefore, whenthe burning state becomes bad in the process of suction air quantityfeedback control and the shift position is changed while ignition timingfeedback control is being conducted, the target engine speed “tne” andthe ignition timing reference value “mia” are changed, and further thefuel injection quantity is changed by a predetermined value, andfeedback control conducted by ignition timing is continued.

In this connection, concerning this fourteenth embodiment, like thevariation of the ninth embodiment, it is possible to devise a variationin which feedback control is conducted by the fuel injection quantity.However, the explanation will be omitted here.

Embodiment of the Fourth Group

Next, embodiments of the fourth group will be explained below. Eachembodiment of the fourth group relates to an engine speed control unitcharacterized in that: influences given to engine speed feedback controlby a change with time and a difference in individual products can beprevented.

Fifteenth Embodiment

First, the fifteenth embodiment will be explained below. In thisfifteenth embodiment, the burning state is good and the idling enginespeed is subjected to suction air quantity feedback control.

FIG. 32 is a flow chart of the fifth embodiment. In step 15001, it isjudged whether or not the engine is in an idling state. Whether or notthe engine is in an idling state is judged by a signal sent from thethrottle opening degree sensor 4 or the accelerator opening degreesensor 15 and also judged by a signal sent from the vehicle speed sensor31. In step 15002, it is judged whether or not suction air quantityfeedback control of the engine 1 is conducted.

When it is not true in steps 15001, 15002 the program proceeds to step15013. When it is true in both steps 15001 and 15002, the programproceeds to step 15003. In step 15003, the engine speed deviation“dltne”, which is a difference between the target engine speed “tne” andthe actual engine speed “ne”, is found. In step 15004, a correctionvalue of the throttle opening degree corresponding to the engine speeddeviation “dltne” is found from the map shown in FIG. 6 which ispreviously stored in ECU 10. Since this correction value is minute, itis referred to as a throttle opening degree minute correction value andrepresented by “dDTHA”.

Next, in step 15005, a total correction value is found by adding thecorrection value of the this time to the correction value up to thistime. This is simply referred to as a throttle opening degree correctionvalue and represented by “DTHA”.

This throttle opening degree correction value DTHA is added to thereference throttle opening degree value GTHA, which is previously setaccording to the condition, and made to be the execution throttleopening degree THA. This relation can be expressed by GTHA+DTHA=THA.This is executed in step 15012 at last.

However, before the program reaches step 15012, the reference throttleopening degree value GTHA and the throttle opening degree correctionvalue DTHA are learned with respect to the present invention.

Therefore, this learning of the reference throttle opening degree valueGTHA and the throttle opening degree correction value DTHA is explained.First of all, the reference throttle opening degree value GTHA isexplained below.

Even when the same idling engine speed is obtained, work generated bythe engine 1 is different because a load given to the engine 1 isdifferent according to the operating condition of the engine 1.

For example, work generated by the engine 1 is different according tothe engine temperature. Further, work generated by the engine 1 isdifferent according to the state of the air conditioner. Furthermore,when the engine 1 is combined with an automatic transmission, workgenerated by the engine 1 is different according to the shift positionof the automatic transmission, that is, work generated by the engine 1is different according to the shift position such as running positionsof D, 4, 3, 2, L, R and also according to stopping positions of P, N.Accordingly, the reference throttle opening degree GTHA is set withrespect to the combination of these conditions by the results ofexperiments.

FIG. 37 is a map of this reference throttle opening degree.

However, the aforementioned load is different for each engine, andfurther the aforementioned load changes with time. Therefore, thethrottle opening degree correction value DTHA is added to the referencethrottle opening degree correction value GTHA. However, when adifference between the throttle opening degree, which is required for apredetermined engine speed, and the reference throttle opening degree islarge, it takes long time for correction.

Therefore, control of this embodiment is conducted as follows. When thethrottle opening degree correction value is higher (smaller) than apredetermined value, the reference throttle opening degree is made large(small), so that the throttle opening degree correction value isdecreased by a value corresponding to the reference throttle openingdegree which has been increased (decreased).

Accordingly, in step 15006, it is judged whether or not the throttleopening degree correction value DTHA(n) of the present time is higherthan the predetermined value KDTHA. When it is not true in step 15006,it is judged in step 15007 whether or not the throttle openingcorrection value DTHA(n) is lower than the predetermined value −KDTHA.

When it is not true in step 15006 and also it is not true in step 15007,the program proceeds to step 15013 and returns.

When it is true in step 15006, the predetermined shift value dGTHA issubtracted from the reference throttle opening degree GTHA(n) in step15008 so as to find the reference throttle opening degree GTHA(n+1) ofthe next time. In step 15010, the predetermined shift value dGTHA isadded to the throttle opening degree correction value DTHA(n) so as tofind the throttle opening degree correction value DTHA (n+1) of the nexttime. In step 15012, the reference throttle opening degree GTHA(n+1) ofthe next time and the throttle opening degree correction value DTHA(n+1)of the next time are added to each so as to find the throttle openingdegree THA(n+1) of the next time, and then the program proceeds to step15013 and returns.

The renewed reference throttle opening degree GTHA(n) is stored in ECU10 in the form shown in FIG. 9.

When it is true in step 15007, the predetermined shift value dGTHA isadded to the reference throttle opening degree GTHA(n) in step 15009 soas to find the reference throttle opening degree GTHA(n+1) of the nexttime. In step 15011, the predetermined shift value dGTHA is subtractedfrom the throttle opening degree correction value DTHA(n), so as to findthe throttle opening degree correction value DTHA (n+1) of the nexttime. In step 15012, the reference throttle opening degree GTHA(n+1) ofthe next time and the throttle opening degree correction value DTHA(n+1)of the next time are added to each so as to find the throttle openingdegree THA(n+1) of the next time, and then the program proceeds to step15013 and returns.

In this connection, the shift value dGTHA can be set at an arbitraryvalue between dTHA and KDTHA.

The fifteenth embodiment operates as described above. Therefore, aperiod of time necessary for correction can be reduced andcontrollability can be enhanced.

FIG. 36 is a view for explaining control of the above fifteenthembodiment.

Sixteenth Embodiment

FIG. 33 is a flow chart showing the sixteenth embodiment. The sixteenthembodiment operates as follows. In the case where the idling enginespeed is subjected to feedback control by the quantity of suction airand the burning state is bad so that control is changed to feedbackcontrol conducted by the ignition timing, the same learning as that ofthe first embodiment is conducted on this feedback control conducted bythe ignition timing.

In step 16001, in the same manner as that of the fifteenth embodiment,it is judged whether or not it is an idling state. In step 16002, it isjudged whether or not the idling engine speed is in ignition timingfeedback control.

When it is not true in steps 16001 and 16002, the program proceeds tostep 16013. When it is true in both steps 16001 and 16002, the programproceeds to step 16003. In step 16003, the engine speed deviation.“dltne”, which is a difference between the target engine speed “tne” andthe actual engine speed “ne”, is found. In step 16004, the minutecorrection value “dDIA” of ignition timing corresponding to the enginespeed deviation “dltne” is found from the map in FIG. 38 previouslystored in ECU 10.

Next, in step 16005, the ignition timing correction value DIA is foundby adding the correction value of the present time to the correctionvalue up to the present time.

In step 16006, it is judged whether or not the ignition timingcorrection value DIA(n) of the present time exceeds the predeterminedvalue KDIA which has been previously determined. When it is not true instep 16006, it is judged instep 16007 whether or not the ignition timingcorrection value DIA(n) is lower than the predetermined value −KDIA.

When it is not true in step 16006 and also it is not true in step 16007,the program proceeds to step 16013 and returns.

When it is true in step 16006, the predetermined shift value dGIA issubtracted from the reference ignition timing GIA(n) in step 16008 so asto find the reference ignition timing GIA(n+1) of the next time. In step16010, the predetermined shift value dGIA is added to the ignitiontiming correction value DIA(n) so as to find the ignition timingcorrection value DIA (n+1) of the next time. In step 16012, thereference ignition timing GIA(n+1) of the next time and the ignitiontiming correction value DIA(n+1) of the next time are added to each soas to find the ignition timing IA(n+1) of the next time, and then theprogram proceeds to step 16013 and returns.

The renewed reference ignition timing GIA(n) is stored in ECU 10 in theform shown in FIG. 41.

When it is true in step 16007, the predetermined shift value dGIA isadded to the reference ignition timing GIA(n) in step 16009 so as tofind the reference ignition timing GIA(n+1) of the next time. In step16011, the predetermined shift value dGIA is subtracted from theignition timing correction value DIA(n), so as to find the ignitiontiming correction value DIA (n+1) of the next time. In step 16012, thereference ignition timing GIA(n+1) of the next time and the ignitiontiming correction value DIA(n+1) of the next time are added to eachother so as to find the ignition timing IA(n+1) of the next time, andthen the program proceeds to step 16013 and returns.

In this connection, the shift value dGIA can be set at an arbitraryvalue between dIA and KDIA.

The sixteenth embodiment operates as described above. Therefore, aperiod of time necessary for correction can be reduced andcontrollability can be enhanced in the same manner as that of the firstembodiment.

Seventeenth Embodiment

FIG. 34 is a flow chart of the seventeenth embodiment. In thisseventeenth embodiment, when the idling engine speed is subjected tofeedback control by the quantity of suction air and the burning state isbad so that feedback control by the quantity of suction air is changedover to feedback control by the quantity of fuel injection, the samelearning as that of the first embodiment is conducted on this feedbackcontrol by the quantity of fuel injection.

In step 17001, in the same manner as that of the fifteenth embodiment,it is judged whether or not the engine is in an idling state. In step17002, it is judged whether or not the idling engine speed is subjectedto feedback control conducted by the quantity of fuel injection.

When it is not true in steps 17001, 17002, the program proceeds to step17013. When it is true in both steps 17001 and 17002, the programproceeds to step 1703. In step 17003, the engine speed deviation“dltne”, which is a difference between the target engine speed “tne” andthe actual engine speed “ne”, is found. In step 17004, a minutecorrection value dDTAU of the quantity of fuel injection correspondingto the engine speed deviation “dltne” is found from the map shown inFIG. 39 which is previously stored in ECU 10.

Next, in step 17005, the throttle opening degree correction value DTAUis found by adding the correction value of the this time to thecorrection value up to this time.

In step 17006, it is judged whether or not the fuel injection quantitycorrection value DTAU(n) of the present time is higher than thepredetermined value KDTAU which has been previously determined. When itis not true in step 17006, it is judged in step 17007, whether or notthe fuel injection quantity correction value DTAU(n) is lower than thepredetermined value −KDTAU which has been previously determined.

When it is not true in step 17006 and also it is not true in step 17007,the program proceeds to step 17013 and returns.

When it is true in step 17006, the predetermined shift value dGTAU issubtracted from the reference fuel injection quantity GTAU(n) in step17008 so as to find the reference fuel injection quantity GTAU(n+1) ofthe next time. In step 17010, the predetermined shift value dGTAU isadded to the fuel injection quantity correction value DTAU(n) so as tofind the fuel injection quantity correction value DTAU (n+1) of the nexttime. In step 17012, the reference fuel injection quantity GTAU(n+1) ofthe next time and the fuel injection quantity correction value DTAU(n+1)of the next time are added to each so as to find the fuel injectionquantity TAU(n+1) of the next time, and then the program proceeds tostep 17013 and returns.

The renewed reference fuel injection quantity GTAU(n) is stored in ECU10 in the form shown in FIG. 40.

When it is true in step 17007, the predetermined shift value dGTAU isadded to the reference fuel injection quantity GTAU(n) in step 17009 soas to find the reference fuel injection quantity GTAU(n+1) of the nexttime. In step 17011, the predetermined shift value dGTAU is subtractedfrom the fuel injection quantity correction value DTAU(n) so as to findthe fuel injection quantity correction value DTAU (n+1) of the nexttime. In step 17012, the reference fuel injection quantity GTAU(n+1) ofthe next time and the fuel injection quantity correction value DTAU(n+1)of the next time are added to each so as to find the fuel injectionquantity TAU(n+1) of the next time, and then the program proceeds tostep 17013 and returns.

In this connection, the shift value dGTAU can beset at an arbitraryvalue between dTAU and KDTAU.

The seventeenth embodiment operates as described above. Therefore, aperiod of time necessary for correction can be reduced andcontrollability can be enhanced in the same manner as that of thefifteenth embodiment.

Eighteenth Embodiment

In this eighteenth embodiment, when the burning state is judged to bebad in feedback control conducted by the idling engine speed, feedbackcontrol conducted by the ignition timing is executed. In this control, acylinder in a bad burning state is discriminated, and ignition timingfeedback control is executed only for that cylinder.

FIG. 35 is a flow chart for controlling the eighteenth embodiment. Steps18001 to 18013 in this flow chart are essentially the same as steps16001 to 16013 in the flow chart of the sixteenth embodiment. However,the following two points are different. One point is that step 18003A todiscriminate a cylinder in the bad burning state is added after step18004, and the other point is that steps 18003 to 18012 are executedonly for a cylinder in a bad burning state.

In this connection, as described before, the cylinder is discriminatedin such a manner that a period of time (angle) that has passed from thereference signal generated by the cam position sensor 30 is measured onthe basis of the signal generated by the crank position sensor 21.

In the eighteenth embodiment, when the burning state is bad in suctionair quantity feedback control and ignition timing feedback control isconducted, a cylinder in a bad burning state is specified, and ignitiontiming feedback control is conducted on that cylinder, and ignitiontiming feedback control is not conducted on other cylinders for whichignition timing feedback control is unnecessary. Therefore, it ispossible to prevent the deterioration of exhaust gas and drivabilitycaused by taking a redundant countermeasure.

In this connection, the above method, in which a cylinder, the burningstate of which is bad even if suction air quantity feedback control isconducted, is specified and subjected to another control, can be appliedto not only the sixteenth embodiment but also the seventeenthembodiment.

Explanations are made into three embodiments belonging to the fourthgroup in which the idling engine speed is controlled. However, thiscontrol can be applied to not only control of the idling engine speedbut also control of the engine speed in another operating condition.

What is claimed is:
 1. An engine speed control unit of an internal combustion engine for controlling an engine speed so that it can reach a target, comprising: a first engine speed control means for controlling the engine speed by changing a quantity of suction air; a second engine speed control means for controlling the engine speed by changing a control value of a control parameter except for the quantity of suction air; and means for judging a burning state, wherein in the case of a good burning state the engine speed is controlled by the first engine speed control means, and in the case of a bad burning state, the engine speed control by the first engine speed control means is stopped and the engine speed is controlled by the second engine speed control means.
 2. An engine speed control unit of an internal combustion engine according to claim 1, wherein the first engine speed control means is made to be a first after-start engine speed control means for controlling the after-start engine speed, which is an engine speed from the completion of the initial combustion at the engine starting to the idling steady state, so that the after-start engine speed can show a target change characteristic in the case where the burning state is judged to be good, the second engine speed control means is made to be a second after-start engine speed control means for controlling the after-start engine speed, which is an engine speed from the completion of the initial combustion at the engine starting to the idling steady state, so that the after-start engine speed can show a target change characteristic in the case where the burning state is judged to be bad, and the after-start engine speed from the completion of the initial combustion at the engine starting to the idling steady state is controlled.
 3. An engine speed control unit of an internal combustion engine according to claim 2, wherein the second after-start engine speed control means changes at least one of the control values of ignition timing, quantity of fuel injection and fuel injection timing.
 4. An engine speed control unit of an internal combustion engine according to claim 2, further comprising a bad burning cylinder judgment means, for judging a cylinder of bad burning, wherein, when it is judged to be a bad burning state, the bad burning cylinder is distinguished from other cylinders and controlled by the second after-start engine speed control means so that the engine speed can show a target change characteristic.
 5. An engine speed control unit of an internal combustion engine according to claim 1, wherein the first engine speed control means is made to be a first idling engine speed control means for controlling the engine speed in the idling steady state so that it can reach the target value by feedback control in the case where the burning state is judged to be good, the second engine speed control means is made to be a second idling engine speed control means for controlling the engine speed in the idling steady state so that it can reach the target value in the case where the burning state is judged to be bad, and the engine speed in the idling steady state is controlled so that it can reach the target value.
 6. An engine speed control unit of an internal combustion engine according to claim 5, wherein when it is judged to be a bad burning state and the idling engine speed control by the first idling engine speed control means is stopped and the idling engine speed control by the second idling engine speed control means is executed, the feedback control by the first idling engine speed control means is executed again after that, the burning state is rejudged by the means for judging a burning state in this state, when it is judged to be a bad burning state in the rejudgment of the burning state, the idling engine speed control is executed by the second engine speed control means.
 7. An engine speed control unit of an internal combustion engine according to claim 6, wherein the idling engine speed control executed by the second engine speed control means after the rejudgment of the burning state is conducted by the same parameter as that of the idling engine speed control executed by the second engine speed control means before the rejudgment of the burning state while the control value is being changed.
 8. An engine speed control unit of an internal combustion engine according to claim 6, wherein the idling engine speed control executed by the second engine speed control means after the rejudgment of the burning state is conducted by a different parameter from that of the idling engine speed control executed by the second engine speed control means before the rejudgment of the burning state.
 9. An engine speed control unit of an internal combustion engine according to claim 8, wherein the idling engine speed control conducted by the second engine speed control means before the rejudgment of the burning state and the idling engine speed control conducted by the second engine speed control means after the rejudgment of the burning state are executed being selected so that the idling engine speed control, the influence given to exhaust gas emission of which is smaller, is executed first.
 10. An engine speed control unit of an internal combustion engine according to claim 5, further comprising a bad burning cylinder discrimination means for discriminating a cylinder in a bad burning state, wherein, when it is judged to be a bad burning state, the bad burning cylinder is discriminated from other cylinders and controlled by the second engine speed control means.
 11. An engine speed control unit of an internal combustion engine according to claim 5, wherein the idling engine speed control conducted by the second engine speed control means is also feedback control.
 12. An engine speed control unit of an internal combustion engine according to claim 5, wherein the idling engine speed control conducted by the second engine speed control means is a quantitative change control by which the control parameter is changed by a predetermined value so that the control parameter can not exceed a guard value.
 13. An engine speed control unit of an internal combustion engine according to claim 5, wherein the internal combustion engine is provided with an air/fuel ratio feedback control means for controlling an air/fuel ratio by feedback control, and the idling engine speed is controlled by the first idling engine speed control means when the air/fuel ratio feedback control means is operated.
 14. An engine speed control unit of an internal combustion engine according to claim 5, wherein the idling engine speed is controlled by the first idling engine speed control means when the engine temperature is higher than a predetermined value.
 15. An engine speed control unit of an internal combustion engine according to claim 5, wherein the idling engine speed is controlled by the first idling engine speed control means when the lapse of time after the start of the engine is more than a predetermined value.
 16. An engine speed control unit of an internal combustion engine according to claim 5, wherein the means for judging a burning state judges a burning state from a change in the engine speed with respect to a change in the quantity of suction air of feedback control conducted by the first engine speed control means.
 17. An engine speed control unit of an internal combustion engine according to claim 1, wherein the first engine speed control means conducts feedback-control so that the engine speed in the idling steady state can be a target value when it is judged to be a good burning state, and the second engine speed control means continues feedback-control so that the engine speed can be an after-load-change engine speed target value, which has been previously set, when a load is changed in the process of executing engine speed control by the second engine speed control means.
 18. An engine speed control unit of an internal combustion engine according to claim 17, wherein the after-load-change engine speed target value is the same as the before-load-change engine speed target value.
 19. An engine speed control unit of an internal combustion engine according to claim 17, wherein the after-load-change engine speed target value is different from the before-load-change engine speed target value.
 20. An engine speed control unit of an internal combustion engine according to claim 17, further comprising a load change detection means, wherein the after-load-change engine speed target value is determined by a change in the load.
 21. An engine speed control unit of an internal combustion engine according to claim 17, wherein the after-load-change control reference value corresponding to the after-load change engine speed target value is set, and the second engine speed control means conducts feedback control on the basis of the after-load-change control reference value.
 22. An engine speed control unit of an internal combustion engine according to claim 17, further comprising a load change detection means, wherein the after-load-change control reference value is determined by a change in the load.
 23. An engine speed control unit of an internal combustion engine according to claim 17, wherein the second engine speed control means conducts feedback control on the idling engine speed by one of the control parameters of the ignition timing and the quantity of fuel injection before a change in the load, and the second engine speed control means conducts feedback control on the engine speed by the same control parameter as that of before a change in the load even after a change in the load.
 24. An engine speed control unit of an internal combustion engine according to claim 17, wherein the second engine speed control means conducts feedback control on the engine speed by one of the control parameters of the ignition timing and the quantity of fuel injection before a change in the load, and the second engine speed control means conducts feedback control on the engine speed by the same control parameter as that of before a change in the load even after a change in the load, and further a control parameter not participating in feedback control is changed by a predetermined value after a change in the load.
 25. An engine speed control unit of an internal combustion engine according to claim 1, further comprising: a parameter reference value learning means for renewing and storing a parameter reference value according to a state of operation; a parameter correction value calculating means for calculating a parameter correction value necessary for making the engine speed close to a target value; and a parameter control means for controlling a parameter so as to provide a parameter execution value in which the parameter correction value is added to the parameter reference value, wherein the parameter reference value learning means renews a parameter reference value so that the parameter correction value can be reduced in the case where the parameter correction value exceeds a predetermined range, and the engine speed of the internal combustion engine is controlled so that it can reach a target value by feedback control of the control parameter selected according to the state of burning.
 26. An engine speed control unit of an internal combustion engine according to claim 25, wherein the parameter reference value learning means stores a parameter reference value according to at least one of the engine temperature, the shift position of a transmission connected with the engine and the state of operation of the accessories.
 27. An engine speed control unit of an internal combustion engine according to claim 25, wherein a quantity of suction air is selected as a control parameter in the case of a good burning state.
 28. An engine speed control unit of an internal combustion engine according to claim 25, wherein ignition timing or a quantity of fuel injection is selected as a control parameter in the case of a bad burning state. 